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<br />7A - ATTACHMENT NO.3 <br />Saltworks Proposa/- Water Group Summary Report (22 January 2010) Page 42 <br /> <br />3.5.2.4 Liquefaction <br /> <br />Liquefaction describes the behavior of soils that, when loaded, suddenly suffer a <br />transition from a solid state to a liquefied state. Liquefaction is more likely to occur in <br />loose granular soils with poor drainage, such as silty sands, sands, or artificial fill, and <br />shallow water levels, and is associated with seismic shaking. It was a major factor in the <br />damage in San Francisco's Marina District during the 1989 Loma Prieta earthquake. <br />The potential for liquefaction is acknowledged in the OMB Application, which states that <br />liquefaction risks can be reduced to acceptable levels with properly-applied engineering <br />practices, which would be described in detail in the project EIR. Some of these <br />mitigating engineering practices include driving pilings to depths that may pierce or <br />compromise the natural confining clay layers beneath the site and allow denser and <br />shallow saltwater and brines to contaminate the underlying freshwater aquifers. The <br />integrity and continuity of the underlying natural clay layers should not be compromised <br />to avoid downward leakage of overlying saltwater and brines. <br /> <br />3.5.3 Conclusions Regarding Groundwater <br /> <br />OMB identified groundwater as the source of 700 AFY, and subsequently revised the <br />water supply proposal so that groundwater is considered a potential backup supply <br />source. This is consistent with the City's 2005 UWMP, which does not consider <br />groundwater to be a source of potable supply for the City because of water quality, <br />reliability, and long-term production capacity concerns . Because the Saltworks project <br />may need to rely on a range of water supply options, the viability of groundwater as a <br />supply source at the site was evaluated. The water team concludes that insufficient <br />information is available to confirm the feasibility of obtaining 700 AFY at the site. OMB <br />indicated that reverse osmosis would be needed to treat groundwater, and the water <br />team concurs that treatment of this type would likely be needed. Substantial additional <br />study would be needed to establish the reliable groundwater yield and impacts of <br />groundwater pumping. <br /> <br />3.6 Graywater and Rainwater Supply <br /> <br />The Saltworks project's primary source of non-potable supply is recycled water. The <br />OMB Supply Report also evaluates both graywater and rainwater as non-potable supply <br />sources to potentially supplement recycled water, and possibly serve some sources in a <br />more effective way. The OMB Supply Report also develops these supply options in case <br />community/public opposition to the use of recycled water for residential irrigation and <br />toilet flushing should arise. <br /> <br />City staff has informed the authors of this report that they would not consider graywater <br />or rainwater as reliable (firm) supplies to meet the water demands of the project (using <br />the City's Attachment Q methodology). If these supplies are used, backup potable or <br />recycled water would need to be available to serve the demands. The City does not, <br />however, have a regulatory position against their use for the project. <br /> <br />3.6.1 Description of Graywater as a Source of Supply <br />Graywater is untreated wastewater from bathtubs, showers, bathroom washbasins, <br />clothes washing machines (unless washing diapers), and laundry tubs. Graywater does <br />not include wastewater from toilets, kitchen sinks or dishwashers. Use of graywater is <br />regulated in California by Chapter 16 of the California Plumbing Code. <br /> <br />35 <br />